manager/state/raft/storage: fix TestCreateOpenInvalidDirFails

[thaJeztah]

• partially addresses Tests failures on master #2479
• relates to [encryption] NaCL/secretbox + wrapper around etcd wal + snapshot #1701 (which introduced the test)

This test failed on macOS, but passed in CI:

--- FAIL: TestCreateOpenInvalidDirFails (0.00s)
    walwrap_test.go:205:
            Error Trace:	walwrap_test.go:205
            Error:      	An error is expected but got nil.
            Test:       	TestCreateOpenInvalidDirFails
time="2022-11-19T14:36:00Z" level=info msg="repaired WAL error" error="unexpected EOF"
FAIL

It looks like this test was always broken; this test was added in 3e2cebe and running the test from that commit and with the Go version used at the time showed the test was failing;

git checkout 3e2cebe76b8c7e1ae67b89de3b5fa063234edc85

docker run -it --rm -v $(pwd):/go/src/github.com/docker/swarmkit -w /go/src/github.com/docker/swarmkit golang:1.7 sh -c 'go test -v -run TestCreateOpenInvalidDirFails ./manager/state/raft/storage/'

=== RUN   TestCreateOpenInvalidDirFails
--- FAIL: TestCreateOpenInvalidDirFails (0.01s)
        Error Trace:    walwrap_test.go:193
    Error:		An error is expected but got nil.

FAIL
exit status 1
FAIL	github.com/docker/swarmkit/manager/state/raft/storage	0.031s

It took some digging to understand why, but when debugging the error in CI (this part of the test expected an error), it became apparent:

--- FAIL: TestCreateOpenInvalidDirFails (0.00s)
    walwrap_test.go:207:
            Error Trace:	walwrap_test.go:207
            Error:      	Received unexpected error:
                            mkdir /not: permission denied
            Test:       	TestCreateOpenInvalidDirFails
time="2022-11-19T16:55:42Z" level=info msg="repaired WAL error" error="unexpected EOF"

So what happened was that;

• walCryptor.Create() is called, which calls wal.Create() (from go.etcd.io/etcd/server/v3/wal/wal.go).
• wal.Create() creates a new .tmp directory at the same location as the specified path (see https://github.com/etcd-io/etcd/blob/server/v3.5.1/server/wal/wal.go#L110-L127)
• in our case, the directory passed was /not/existing/directory, so it tries to create /not/existing/directory.tmp.
• which fails, because CI doesn't run as root and doesn't have permissions to create the path.

On macOS, running the test inside a container failed, as the tests are run as root inside the container. Similarly, when updating the test to use t.TempDir(), and using /not/existing/directory within that directory, the test failed as well (as there's no permissions issue when creating the .tmp directory inside the temp-dir).

So, in short, the test was broken from the start; calling was.Create() using a non-existing directory is allowed, and not an error condition. (If we do want it to be an error-condition, we should implement code to disallow this).

This patch removes the broken part from the test, and updates the remaining part to use t.TempDir() and a directory inside that's certain to be empty.

Also renaming the test to TestOpenInvalidDirFails, as the test now only covers the Open case.

[thaJeztah]

@corhere @neersighted @dperny PTAL

[codecov-commenter]

Codecov Report

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[thaJeztah]

Thx! Let me bring this one in